AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 82377-384
Tooth Wear and Temporomandibular Joint Change in Australian Aboriginal Populations L.C. RICHARDS Department of Dentistry, The University of Adelaide, Adelaide South Australia 5001
Dental attrition, Degenerative joint changes, FaKEY WORDS cial morphology
ABSTRACT
The masticatory system consists of teeth, temporomandibular joints, and the supporting craniofacial skeleton. The form and function of each of these components of the system can be understood only within the overall context of the system. In a series of studies, the complex relationships between tooth wear and temporomandibular joint morphology and pathology were considered in samples consisting of a total of 58 male and 54 female crania from two Australian Aboriginal populations. The extent and buccolingual direction of tooth wear were assessed using established techniques. Both metric and nonmetric descriptions of temporomandibular joint morphology and pathology were developed. Significant differences in patterns of tooth wear and in the frequencies of various temporomandibular joint changes were evident between sexes and between populations. Furthermore, significant correlations between a number of tooth and joint variables were also evident. In addition, there was clear evidence of relationships between both tooth wear and temporomandibular joint changes and craniofacial morphology. The results of this study provide additional evidence of the complex relationships between the form and function of the masticatory system. The masticatory system is a complex system consisting of teeth, temporomandibular joints, and the supporting craniofacial skeleton. There are significant deficiencies in our knowledge of the individual components of the system and even greater deficiencies in our understanding of the way in which the form and function of the components of the system are related. Detailed theoretical descri tions of the relationship between the teet and the temporomandibular joints were proposed many years ago (e.g., Hanau, 19261, but with few exceptions (e.g., Koyoumdjisky, 1956; Mongini, 1975) the available data have been inconclusive (e.g., An el, 1948). Because of the very igh demands that the Australian aboriginals made on their masticatory systems, studies of these people have provided important information about many of these questions. For example, Be g (1954) developed the theories of dental occ usion on which his clinical orthodontic techni ues were based from his observations of the us-
R
tralian Aborigmals, and Mur hy (1959)used data obtained from Austra\an aboriginal skeletal collections as evidence of the adaptive mechanisms such as continuous tooth eruption and alveolar bone growth acting to maintain face height in the presence of a marked reduction in dental crown height. Previous studies have described the heavy tooth wear generally evident in Australian Aboriginals and have provided consistent evidence of the relative1 large teeth in this oup (Campbell, 1925; arrett et al., 1963; ownsend and Brown, 1979). The available data provide conflicting information about the temporomandibular joints. However,
F
B
fl
f
@ 1990 WILEY-LISS. INC.
x
Received August 12,1988; accepted June 9,1989. Address reprint requests to Dr. L.C. Richards, Department of Dentistry, The University of Adelaide, G.P.O. Box 498, Adelaide, South Australia 5001. This paper was presented as part of the symposium “The Face and Dentition of Australian Po ulations” a t the 57th Annual Meeting, American Association orPhysical Anthropologists, Kansas City, March 1988.
378
L.C. RICHARDS
Duckworth (1904) remarked on the extremely flattened and shallow glenoid fossae in aboriginal Australians, whereas Moffett (1974) and Porowski and Bruska (1978) did not find any significant intergroup differences in the joint dimensions they considered. Similarly conflicting evidence of the relationship between age (or extent of tooth wear) and joint morphology has also been provided, with some studies demonstrating an increase in eminence height with age (Campbell, 19251, some showing a decrease in the height of eminence with advancing tooth wear (Seward, 1976) and others showing more complex relationships (Hinton, 1981). This paper reviews a series of recent studies of tooth wear and temporomandibular joint morphology and pathology (Richards and Brown, 1981a,b, 1986; Richards, 1984, 1985,1987) and provides an overview of the relationships between the components of the masticatory system. MATERIALS AND METHODS
In this study, crania of two populations from the collections of the South Australian Museum were selected. Ages were estimated by the method developed by Richards and Brown (1981a),and sexes were assigned using the discriminant function method described by Giles and Elliot (1963)modified to allow for the different section point. The first group (37 males and 37 females) were from members of the Narrinyeri federation, who occupied the shores of a clearly defined river basin and associated lake system surrounded to the northwest by mountains, to the northeast by a dry and inhospitable hinterland, and to the south by the sea. Even greater than any geographic barriers, however, were the cultural and ritual differences between these people and their neighbours. The western extent of the Narrinyeri area was the eastern limit of the rite of circumcision, and as a result the neighbouring tribes to the west did not regard the Narrinyeri as “real men,” whereas the Narrinyeri regarded their circumcised neighbours as evil spirits (Tindale, 1974). Ta lin (1874) records that the Narrinyeri also ad little regard for their eastern neighbours, who they believed were cannibals. The second group (21 males, 17 females) were all members of the Kaurna tribe living to the west of the Narrinyeri. Although they were neighbouring tribes, the two groups
K
would have had little contact and, in addition, their diet and food preparation habits were different. The Narrinyeri were river and lake dwellers and as such were predominantly fishermen (Taplin, 1874), whereas the coastal-dwelling Kaurna obtained most of their food by hunting and gathering (Cleland, 1966).There were no significant differences in age or sex distributions for the samples. The extent of tooth wear was described for each tooth by the ratio of the area of exposed dentine to the total crown area (Behrand, 1977), which was assessed from standardized photographs. The relative rate of tooth wear was estimated using the residual scores obtained by the principal axis method outlined by Scott (1979)and Richards (1984). Positive scores implied relatively rapid tooth wear, and negative scores were evidence of slower wear than predicted from the wear evident on the maxillary first molar. The direction of wear on mandibular molar teeth was measured using a profile gauge (Richards and Brown, 1986), with ositive angles indicating a relatively bucca orientation of the occlusal surface. Temporomandibular joint morphology was described by a series of simple linear and angular measures, including articular eminence slope relative to the Frankfort horizontal and mandibular condyle diameters (mediolateral and anteroposterior) and orientations. In addition, condyle form was described by dividing the surface into posterior, anterior-medial, and anterior-lateral regions and classifying each area as convex, flat, or concave (Richards, 1987). Pathological changes in the joint were described as mild or severe, depending on whether erosive or proliferative changes affected less than or more than half at the joint surface (Richards and Brown, 1981b). Although not central to the question of the relationshi between the teeth and the temoromandi ular joints, a number of cranioacial variables were associated with both dental and joint variables. Therefore, the cruniofacial morphology of subjects was assessed by standard measurements recorded directly from skulls and indirectly from ce halometric radiographs (Richards, 1985). !he reproducibility of measurements of each variable was assessed and has been reported in detail elsewhere (Richards, 1983). Unless otherwise stated, all analyses were performed using the SPSS-Xpackage of routines.
P
F
B
379
TOOTH WEAR AND JOINT CHANGE
RESULTS
Significant differences in the pattern of tooth wear in males and females from each group were evident (Richards, 1984). In the maxilla, for exam le, the rate of anterior tooth wear (age in ependent) for the Kaurna group was consistently greater than for the Narrinyeri group, whereas the reverse was true for posterior teeth (Fig. 1).Significant differences in craniofacial morphology between the groups have also been described (Richards, 1985) with significantly larger cranial vault lengths and breadths but smaller cranial base dimensions in Narrinyeri males and females. In addition, frontal thickness, zygomatic breadth, and ramus breadth (implying greater muscularity) were all larger in Narrinyeri males, and measures of mandibular prognathism particularly were larger in Narrinyeri males and females. There were also important differences in the correlations between facial measures and the extent of tooth wear with Narrinyeri males (and to a lesser extent Kaurna females), showing marked loss of anterior
a
face height and an increase in mandibular basal prognathism. The observed changes in other groups were much less dramatic, with the loss of interalveolar height associated with extensive attrition being compensated for by maxillary and mandibular changes (Richards, 1985). Significant differences between the groups in joint morphology and patholog were also evident. For example, the morpho ogy of each of the condyle surfaces and the presence of pathological degenerative changes were clearly age dependent (Fig. 2). Considering pooled data for the posterior surface, there were no degenerative changes in the youngest group and only about 25% of subjects showed signs of remodelling. In the middle age group, about 15%showed degenerative changes, and almost 40% showed some remodelling; in the oldest group, the same percentage showed no remodelling, but there was an increased frequency of pathological lesions. A similar tendency was evident for the medial half of the anterior condylar surface and for the lateral surface, where the main difference was in the very high frequency of remodelling changes. This
i
Maxilla 0.2
?!
0
0
cn
0.1
c
0 -
+
MalesA FernalesA Q Males B + FemalesB
c
c L
0.
t m
3
0 m
0.0
al
a
-0.1
i
I1
~
12
i
~
C
Pml
i
~
Pm2
i
M2
-
i
M3
Tooth
Fig. 1. Residual attrition scores (positive score indicates relatively rapid wear) for maxillary teeth of Narrinyeri (A) and Kaurna (B) males and females.
~
i
~
Medial Surface 120
1
100
80
GO
ta e3
Normal Remodelled Pathology
40
20
0 < 39
40
-
59
Age (years)
Posterior Surface
I2O 100
--s
1
80
i
c 0
*
i LL
GO
ka
Normal RernodeOed
Pathology
40
20
0 < 39
40
-
59
>
GO
Age (years)
Lateral Surface
100
-;e
80
2.
c
a,
60
3
0
U
I;
40
20
0 < 39
40
-
59
Age (years)
Normal fiemodellad Parhdogy
381
TOOTH WEAR AND JOINT CHANGE
information needs to be interpreted carefully, however, as these variables were not only age related but also closely related to other dental and facial variables. In addition to significant age differences in 'oint pathology, there were significant diffkrences between populations, with the
incidence of degenerative joint change being highest in Narrinyeri males and lowest in Kaurna males (Fig. 3 ) . In Narrinyeri males almost 20% of the youngest group showed some pathological changes, and more than 30% of the oldest group showed severe changes. In the Kaurna group, none of the
-
Males Narrlnyerl 120
100
0 z
c
80
m
60
0
'y
Y
N
O
~
~
A
ModeraleA Severe A
U 3
40
20
0
Males - Kaurna lZO
I
c39
40
-
59
,w
4 4
Fig. 3. Frequencies of normal, moderately affected by degenerative change and severely affected right temporomandibular joints in Narrinyeri and Kaurna males. Fig. 2. Frequencies of right-side mandibular condyles showing no remodelling (normal), remodelling, and degenerative changes ipathology) of the posterior,
anterior-medial, and anterior-lateral surfaces for pooled Narrinyeri and Kaurna male and female subjects.
382
L.C. RICHARDS
youngest group showed any pathological change, and none from any group showed severe changes. There were a number of significant correlations between the rates of tooth wear and various aspects of joint morphology (Table 1).There was a significant positive correlation between lower anterior tooth wear and eminence slope. Similarly, there was a significant ositive correlation between the angle o f t e condyle in the frontal plane and the rate of upper anterior tooth wear. In addition, there were consistent negative correlations between the anteroposterior diameter of the condyle and the rate of tooth wear. Not only was the rate of tooth wear related to joint morphology, but in addition there were large ositive correlations between the direction orwear on the third molars and the slope of the articular eminence on the same side (r = 0.63 [right side]; r = 0.53 [left side]; P < 0.05). This was associated with the development helicoidal form of the occlusal plane (Richards and Brown, 19861, where the contacts producing wear on the third molar were on the nonchewing side, and so
K
TABLE 1. Correlations between residual attribution scores for canine (C) and second premolar teeth (Pm2) and temDoromandibular joint variables
C Eminence slope Frontal angle Transverse angle A-P diameter M-L diameter
Maxilla Pm2
0.18 0.33 -0.03 -0.34* -0.12
0.12 0.12 0.02 -0.43* -0.11
Mandible Pm2
C
0.34* 0.17 -0.09 -0.24 0.02
*P < 0.05.
the direction that the mandible moved while producing that wear was under the very direct influence of the adjacent joint, whereas the wear on the chewing side was less directly influenced. The pattern of tooth wear also differed between those with and without signs of pathoZogicaZ joint change (Fig. 4). In the maxilla, for example, the rate of anterior tooth wear was significantly higher in affected subjects, whereas the rates of posterior tooth wear were significantly lower. In addition, certain individuals with a characteristic facial morphology were very prone to
Maxilla 0.10
,
-0.05 I1
12
-0.08 -0.03 -0.39* -0.39" 0.23
C
PM1
PM2
M2
Tooth Fig. 4. Residual attrition scores (positive score indicates relatively rapid wear) for maxillary teeth in normal subjects affected by degenerative temporomandibular joint change.
383
TOOTH WEAR AND JOINT CHANGE
pathological change. Of 27 subjects with relatively small ramus dimensions and either large occlusal plane angles and small facial profile angles or small occlusal plane angles and large facial profile angles, 23 showed signs of athological joint change, compared with o n y 27 of the remaining 79 in the sample.
P
DISCUSSION
The results of this series of studies are significant for at least two reasons. In general, they illustrate the relationshi s between the teeth, facial skeleton, anCY temporomandibular joints, which are significant in a number of clinical areas and which are also important in the interpretation of data from studies of individual components of the masticatory system. The specific details of these relationships are also significant in that they provide important evidence about the relationship between the form and the function of the masticatory system. The tooth-wear studies (Richards, 1984, 1985) su port Molnar’s (1972) general contention t at patterns of tooth wear reflect dietary and cultural differences with more rapid anterior tooth wear in the coastal dwelling Kaurna hunter-gatherers than in the Narrinyeri fishermen. The tooth wear data also confirm Murphy’s (1959) model of adaptation to loss of interalveolar hei ht b compensatory maxillary and mandibu ar a veolar bone changes. Mur hy’s model has been extended by the ad I fition of a more extensive series of craniofacial measurements, which suggest that this compensation is least effective in very muscular individuals with rapid posterior tooth wear (Narrinyeri males) and in relatively retrognathic individuals with rapid anterior tooth wear (Kaurna females). The complexities of the masticatory system are most evident in the relationships between both the patterns of tooth wear and craniofacial morphology and the morphology and pathology of the temporomandibular joints. The determinants of joint morphology are not well described, and although the studies described here (Richards, 1987) provide evidence of associations between aspects ofjoint morphology and both tooth wear and facial form, a comprehensive model of the determinants of joint morphology has not emerged. The factors that determine the nature and extent of joint remodelling are also poorly
R
Y P
described. Both the articular eminence and mandibular condyle show a e-related changes, with eminence heig t being smaller in older individuals, supporting the general conclusions reached by Seward (1976), and the frequency of condyle remodelling increasing with age. In addition, condyle remodelling was more commonly seen in individuals with relatively rapid anterior tooth wear, supporting the obvious conclusion that functional differences should be associated with differences in the pattern of joint remodelling. Many questions about the determinants of joint morphology are as yet unanswered, however. A clearer idea of the factors involved in the development of pathological joint changes in these groups has emerged from this series of studies (Richards and Brown, 1981b; Richards, 1988).Not only are the changes clearly age-dependent, but they are seen much more frequently in the groups showing the least effective mechanisms for compensating for rapid tooth wear (Narrinyeri males and Kaurna females) and in groups showing very rapid posterior tooth wear (Narrinyeri males and females). In addition, individuals with certain facial types (small ramus dimensions and either large facial profile angles and small occlusal plane angles or large occlusal plane angles and small facial profile angles) were very likely to be affected, indicating that both dental and facial factors were associated with the development of degenerative lesions of the temporomandibular joints. Despite the significant findings in this series of studies, investigations of this type are not without very important limitations. The nature of the available material means that most of the information was obtained from correlation analyses of cross-sectional data. This not only means that age-dependent variables must be interpreted carefully because of the possibility of sampling differences between the age groups, but also largely excludes the possibility of establishing cause-effect relationships between variables. For example, the observed correlation between articular eminence slope and the orientation of the occlusal surface of the ipsilateral third molars is a very important factor in the development of the helicoidal plane and is arguably an important factor in protecting the joint against excessive loading. Based on available information, however, the observed association provides no information about whether established joint
a
384
L.C. RICHARDS
morphology and the resultant pattern of mandibular movement is determining the direction of tooth wear or whether the joint is adapting to the pattern of movement determined by the teeth. The complex, multivariate nature of the questions addressed can also complicate both the design of studies such as this and interpretation of the results. The problems of missing data in studies of skeletal material and the combination of metric and nonmetric variables limit the usefulness of powerful multivariate statistical methods (Kowalski, 1972). Moreover, the very large sample sizes that would probably be required to demonstrate the significance of various, less common facial forms in the development of pathological joint lesions are either not available, or the necessary data collection would be prohibitively time consuming. Despite the difficulties in interpreting some of the information, these studies have rovided valuable support for some previous Rypotheses, the cast doubt on some other proposals, and t ey provided a rich source of promising new ideas for future investigation.
i
ACKNOWLEDGMENTS
This work was supported in part by the National Health and Medical Research Council of Australia and The University of Adelaide. The advice and assistance of Professor Tasman Brown, Dr. Grant Townsend, Professor Stephen Molnar, Mrs. Sandra Pinkerton, Mrs. Shirley Hastings, Dr. Diana Fabijan, Dr. Helen Bondarenko, Miss Fiona Rowett, Mrs. Wendy Schwerdt, and the Board and staff of the South Australian Museum are gratefully acknowledged. LITERATURE CITED Angel J L (1941) Factors in temporomandibular joint form. Am. J. Anat. 83:223-246. Barrett MJ, Brown T, and Macdonald MR (1963) Dental observations of Australian Aborigines: a roentgenographic study of prognathism. Aust. Dent. J. 8:418427. Begg PR (1954) Stone age man's dentition. Am. J . Orthod. 40:298-312. Behrand GD (1977) Quantitative evaluation of dental attrition (Abstract).Am. J. Phys. Anthropol. 47:117. Campbell TD (1925) Dentition and palate of the Australian Aboriginal. Adelaide: Sheridan Foundation. Cleland J B (1966)The ecology of the Aboriginal in south and central Australia. In BC Cotton (ed): Aboriginal Man in South and Central Australia. Adelaide: Government Printer, pp. 111-158. Duckworth WLH (1904) Morphology and anthropology. Cambridge: Cambridge University Press.
Giles E and Elliot 0 (1963) Sex determination by discriminant function analysis of crania. Am. J. Phys. Anthrop. 21:53-68. Hanau RL (1926) Articulation defined, analyzed and formulated. J. Am. Dent. Assoc. 13:1694-1709. Hinton RJ (1981) Changes in articular eminence morphology with dental function. Am. J . Phys. Anthropol. 54:439-455. Kowalsi CJ (1972)Acommentaryon the use ofmultivariate statistical methods in anthropological research. Am. J. Phys. Anthropol. 36:119-132. Koyoumdjisky E (1956) The correlation of the inclined planes of the articular surface of the glenoid fossa with the cuspal and palatal slopes of the teeth. J. Dent. Res. 35:890-901. Moffett BC (1974) The temporomandibular joint. In JJ Sharry (ed): Complete Denture Prosthodontics (3rd edition). New York: McGraw-Hill, pp. 56-104. Molnar S (1972) Tooth wear and culture-a survey of tooth functions among prehistoric populations. Curr. Anthropol. 13:511-526. Mongini F (1975) Dental abrasion as a factor in remodelling of the mandibular condyle. Acta Anat. 82: 292-300. Murphy TR (1959) Compensatory mechanisms in face height adjustment to functional tooth attrition. Am. J. Phys. Anthropol. 17:312-323. Porowski L and Bruska M (1978)Morphology of mandibular head of skulls from Uganda, Australia and Milicz. Folia Morphol. 37: 407-4 14. Richards LC (1983) Adaptation in the Masticatory System. Descriptive and Correlative Studies of a Precontemporary Population. Ph.D. thesis. The University of Adelaide. Richards LC (1984) Principal axis analysis of dental attrition data from two Australian Aboriginal populations. Am. J. Phys. Anthropol. 65:5-13. Richards LC (1985) Dental attrition and craniofacial morphology in two Australian Aboriginal populations. J . Dent. Res. 64:1311-1315. Richards LC (1987) Temporomandibular joint morphology in two Australian Aboriginal populations. J. Dent. Res. 66:1602-1 607. Richards LC (1988) Degenerative changes in the temporomandibular joint in two Australian Aboriginal populations. J . Dent. Res. 67:1529-1533. Richards LC and Brown T (1981a) Dental attrition and a e relationships in Australian Aborignals. Archaeol. ys. Anthropol. Oceania 16:94-98. Richards LC and Brown T (1981b) Dental attrition and degenerative arthritis of the temporomandibular joint. J . Oral Rehab. 8:293-307. Richards LC and Brown T (1986) Development of the helicoidal plane. Hum. Evol. 1:385-398. Scott EC (1979)Principal axis analysis of attrition data. Am. J . Phys. Anthropol. 51:203-212. Seward FS (1976)Tooth attrition and the temporomandibular joint. Angle Orthod. 46t162-170. Taplin GT (1874) The Narrinyeri, an account of the tribes of South Australian Aborigines inhabiting the country around the lakes Alexandrina, Albert and Coorong, and the lower part ofthe Murray River: Their manners and customs. Adelaide: Sawyer. Tindale NB (1974) Aboriginal tribes of Australia. Canberra: Australian National University Press. Townsend GC and Brown T (1979) Tooth size and characteristics ofAustralian Aborigines. Occ. Papers Hum. Biol. 1:17-38.
PI
Tooth Wear and Temporomandibular Joint Change in Australian Aboriginal Populations L.C. RICHARDS Department of Dentistry, The University of Adelaide, Adelaide South Australia 5001
Dental attrition, Degenerative joint changes, FaKEY WORDS cial morphology
ABSTRACT
The masticatory system consists of teeth, temporomandibular joints, and the supporting craniofacial skeleton. The form and function of each of these components of the system can be understood only within the overall context of the system. In a series of studies, the complex relationships between tooth wear and temporomandibular joint morphology and pathology were considered in samples consisting of a total of 58 male and 54 female crania from two Australian Aboriginal populations. The extent and buccolingual direction of tooth wear were assessed using established techniques. Both metric and nonmetric descriptions of temporomandibular joint morphology and pathology were developed. Significant differences in patterns of tooth wear and in the frequencies of various temporomandibular joint changes were evident between sexes and between populations. Furthermore, significant correlations between a number of tooth and joint variables were also evident. In addition, there was clear evidence of relationships between both tooth wear and temporomandibular joint changes and craniofacial morphology. The results of this study provide additional evidence of the complex relationships between the form and function of the masticatory system. The masticatory system is a complex system consisting of teeth, temporomandibular joints, and the supporting craniofacial skeleton. There are significant deficiencies in our knowledge of the individual components of the system and even greater deficiencies in our understanding of the way in which the form and function of the components of the system are related. Detailed theoretical descri tions of the relationship between the teet and the temporomandibular joints were proposed many years ago (e.g., Hanau, 19261, but with few exceptions (e.g., Koyoumdjisky, 1956; Mongini, 1975) the available data have been inconclusive (e.g., An el, 1948). Because of the very igh demands that the Australian aboriginals made on their masticatory systems, studies of these people have provided important information about many of these questions. For example, Be g (1954) developed the theories of dental occ usion on which his clinical orthodontic techni ues were based from his observations of the us-
R
tralian Aborigmals, and Mur hy (1959)used data obtained from Austra\an aboriginal skeletal collections as evidence of the adaptive mechanisms such as continuous tooth eruption and alveolar bone growth acting to maintain face height in the presence of a marked reduction in dental crown height. Previous studies have described the heavy tooth wear generally evident in Australian Aboriginals and have provided consistent evidence of the relative1 large teeth in this oup (Campbell, 1925; arrett et al., 1963; ownsend and Brown, 1979). The available data provide conflicting information about the temporomandibular joints. However,
F
B
fl
f
@ 1990 WILEY-LISS. INC.
x
Received August 12,1988; accepted June 9,1989. Address reprint requests to Dr. L.C. Richards, Department of Dentistry, The University of Adelaide, G.P.O. Box 498, Adelaide, South Australia 5001. This paper was presented as part of the symposium “The Face and Dentition of Australian Po ulations” a t the 57th Annual Meeting, American Association orPhysical Anthropologists, Kansas City, March 1988.
378
L.C. RICHARDS
Duckworth (1904) remarked on the extremely flattened and shallow glenoid fossae in aboriginal Australians, whereas Moffett (1974) and Porowski and Bruska (1978) did not find any significant intergroup differences in the joint dimensions they considered. Similarly conflicting evidence of the relationship between age (or extent of tooth wear) and joint morphology has also been provided, with some studies demonstrating an increase in eminence height with age (Campbell, 19251, some showing a decrease in the height of eminence with advancing tooth wear (Seward, 1976) and others showing more complex relationships (Hinton, 1981). This paper reviews a series of recent studies of tooth wear and temporomandibular joint morphology and pathology (Richards and Brown, 1981a,b, 1986; Richards, 1984, 1985,1987) and provides an overview of the relationships between the components of the masticatory system. MATERIALS AND METHODS
In this study, crania of two populations from the collections of the South Australian Museum were selected. Ages were estimated by the method developed by Richards and Brown (1981a),and sexes were assigned using the discriminant function method described by Giles and Elliot (1963)modified to allow for the different section point. The first group (37 males and 37 females) were from members of the Narrinyeri federation, who occupied the shores of a clearly defined river basin and associated lake system surrounded to the northwest by mountains, to the northeast by a dry and inhospitable hinterland, and to the south by the sea. Even greater than any geographic barriers, however, were the cultural and ritual differences between these people and their neighbours. The western extent of the Narrinyeri area was the eastern limit of the rite of circumcision, and as a result the neighbouring tribes to the west did not regard the Narrinyeri as “real men,” whereas the Narrinyeri regarded their circumcised neighbours as evil spirits (Tindale, 1974). Ta lin (1874) records that the Narrinyeri also ad little regard for their eastern neighbours, who they believed were cannibals. The second group (21 males, 17 females) were all members of the Kaurna tribe living to the west of the Narrinyeri. Although they were neighbouring tribes, the two groups
K
would have had little contact and, in addition, their diet and food preparation habits were different. The Narrinyeri were river and lake dwellers and as such were predominantly fishermen (Taplin, 1874), whereas the coastal-dwelling Kaurna obtained most of their food by hunting and gathering (Cleland, 1966).There were no significant differences in age or sex distributions for the samples. The extent of tooth wear was described for each tooth by the ratio of the area of exposed dentine to the total crown area (Behrand, 1977), which was assessed from standardized photographs. The relative rate of tooth wear was estimated using the residual scores obtained by the principal axis method outlined by Scott (1979)and Richards (1984). Positive scores implied relatively rapid tooth wear, and negative scores were evidence of slower wear than predicted from the wear evident on the maxillary first molar. The direction of wear on mandibular molar teeth was measured using a profile gauge (Richards and Brown, 1986), with ositive angles indicating a relatively bucca orientation of the occlusal surface. Temporomandibular joint morphology was described by a series of simple linear and angular measures, including articular eminence slope relative to the Frankfort horizontal and mandibular condyle diameters (mediolateral and anteroposterior) and orientations. In addition, condyle form was described by dividing the surface into posterior, anterior-medial, and anterior-lateral regions and classifying each area as convex, flat, or concave (Richards, 1987). Pathological changes in the joint were described as mild or severe, depending on whether erosive or proliferative changes affected less than or more than half at the joint surface (Richards and Brown, 1981b). Although not central to the question of the relationshi between the teeth and the temoromandi ular joints, a number of cranioacial variables were associated with both dental and joint variables. Therefore, the cruniofacial morphology of subjects was assessed by standard measurements recorded directly from skulls and indirectly from ce halometric radiographs (Richards, 1985). !he reproducibility of measurements of each variable was assessed and has been reported in detail elsewhere (Richards, 1983). Unless otherwise stated, all analyses were performed using the SPSS-Xpackage of routines.
P
F
B
379
TOOTH WEAR AND JOINT CHANGE
RESULTS
Significant differences in the pattern of tooth wear in males and females from each group were evident (Richards, 1984). In the maxilla, for exam le, the rate of anterior tooth wear (age in ependent) for the Kaurna group was consistently greater than for the Narrinyeri group, whereas the reverse was true for posterior teeth (Fig. 1).Significant differences in craniofacial morphology between the groups have also been described (Richards, 1985) with significantly larger cranial vault lengths and breadths but smaller cranial base dimensions in Narrinyeri males and females. In addition, frontal thickness, zygomatic breadth, and ramus breadth (implying greater muscularity) were all larger in Narrinyeri males, and measures of mandibular prognathism particularly were larger in Narrinyeri males and females. There were also important differences in the correlations between facial measures and the extent of tooth wear with Narrinyeri males (and to a lesser extent Kaurna females), showing marked loss of anterior
a
face height and an increase in mandibular basal prognathism. The observed changes in other groups were much less dramatic, with the loss of interalveolar height associated with extensive attrition being compensated for by maxillary and mandibular changes (Richards, 1985). Significant differences between the groups in joint morphology and patholog were also evident. For example, the morpho ogy of each of the condyle surfaces and the presence of pathological degenerative changes were clearly age dependent (Fig. 2). Considering pooled data for the posterior surface, there were no degenerative changes in the youngest group and only about 25% of subjects showed signs of remodelling. In the middle age group, about 15%showed degenerative changes, and almost 40% showed some remodelling; in the oldest group, the same percentage showed no remodelling, but there was an increased frequency of pathological lesions. A similar tendency was evident for the medial half of the anterior condylar surface and for the lateral surface, where the main difference was in the very high frequency of remodelling changes. This
i
Maxilla 0.2
?!
0
0
cn
0.1
c
0 -
+
MalesA FernalesA Q Males B + FemalesB
c
c L
0.
t m
3
0 m
0.0
al
a
-0.1
i
I1
~
12
i
~
C
Pml
i
~
Pm2
i
M2
-
i
M3
Tooth
Fig. 1. Residual attrition scores (positive score indicates relatively rapid wear) for maxillary teeth of Narrinyeri (A) and Kaurna (B) males and females.
~
i
~
Medial Surface 120
1
100
80
GO
ta e3
Normal Remodelled Pathology
40
20
0 < 39
40
-
59
Age (years)
Posterior Surface
I2O 100
--s
1
80
i
c 0
*
i LL
GO
ka
Normal RernodeOed
Pathology
40
20
0 < 39
40
-
59
>
GO
Age (years)
Lateral Surface
100
-;e
80
2.
c
a,
60
3
0
U
I;
40
20
0 < 39
40
-
59
Age (years)
Normal fiemodellad Parhdogy
381
TOOTH WEAR AND JOINT CHANGE
information needs to be interpreted carefully, however, as these variables were not only age related but also closely related to other dental and facial variables. In addition to significant age differences in 'oint pathology, there were significant diffkrences between populations, with the
incidence of degenerative joint change being highest in Narrinyeri males and lowest in Kaurna males (Fig. 3 ) . In Narrinyeri males almost 20% of the youngest group showed some pathological changes, and more than 30% of the oldest group showed severe changes. In the Kaurna group, none of the
-
Males Narrlnyerl 120
100
0 z
c
80
m
60
0
'y
Y
N
O
~
~
A
ModeraleA Severe A
U 3
40
20
0
Males - Kaurna lZO
I
c39
40
-
59
,w
4 4
Fig. 3. Frequencies of normal, moderately affected by degenerative change and severely affected right temporomandibular joints in Narrinyeri and Kaurna males. Fig. 2. Frequencies of right-side mandibular condyles showing no remodelling (normal), remodelling, and degenerative changes ipathology) of the posterior,
anterior-medial, and anterior-lateral surfaces for pooled Narrinyeri and Kaurna male and female subjects.
382
L.C. RICHARDS
youngest group showed any pathological change, and none from any group showed severe changes. There were a number of significant correlations between the rates of tooth wear and various aspects of joint morphology (Table 1).There was a significant positive correlation between lower anterior tooth wear and eminence slope. Similarly, there was a significant ositive correlation between the angle o f t e condyle in the frontal plane and the rate of upper anterior tooth wear. In addition, there were consistent negative correlations between the anteroposterior diameter of the condyle and the rate of tooth wear. Not only was the rate of tooth wear related to joint morphology, but in addition there were large ositive correlations between the direction orwear on the third molars and the slope of the articular eminence on the same side (r = 0.63 [right side]; r = 0.53 [left side]; P < 0.05). This was associated with the development helicoidal form of the occlusal plane (Richards and Brown, 19861, where the contacts producing wear on the third molar were on the nonchewing side, and so
K
TABLE 1. Correlations between residual attribution scores for canine (C) and second premolar teeth (Pm2) and temDoromandibular joint variables
C Eminence slope Frontal angle Transverse angle A-P diameter M-L diameter
Maxilla Pm2
0.18 0.33 -0.03 -0.34* -0.12
0.12 0.12 0.02 -0.43* -0.11
Mandible Pm2
C
0.34* 0.17 -0.09 -0.24 0.02
*P < 0.05.
the direction that the mandible moved while producing that wear was under the very direct influence of the adjacent joint, whereas the wear on the chewing side was less directly influenced. The pattern of tooth wear also differed between those with and without signs of pathoZogicaZ joint change (Fig. 4). In the maxilla, for example, the rate of anterior tooth wear was significantly higher in affected subjects, whereas the rates of posterior tooth wear were significantly lower. In addition, certain individuals with a characteristic facial morphology were very prone to
Maxilla 0.10
,
-0.05 I1
12
-0.08 -0.03 -0.39* -0.39" 0.23
C
PM1
PM2
M2
Tooth Fig. 4. Residual attrition scores (positive score indicates relatively rapid wear) for maxillary teeth in normal subjects affected by degenerative temporomandibular joint change.
383
TOOTH WEAR AND JOINT CHANGE
pathological change. Of 27 subjects with relatively small ramus dimensions and either large occlusal plane angles and small facial profile angles or small occlusal plane angles and large facial profile angles, 23 showed signs of athological joint change, compared with o n y 27 of the remaining 79 in the sample.
P
DISCUSSION
The results of this series of studies are significant for at least two reasons. In general, they illustrate the relationshi s between the teeth, facial skeleton, anCY temporomandibular joints, which are significant in a number of clinical areas and which are also important in the interpretation of data from studies of individual components of the masticatory system. The specific details of these relationships are also significant in that they provide important evidence about the relationship between the form and the function of the masticatory system. The tooth-wear studies (Richards, 1984, 1985) su port Molnar’s (1972) general contention t at patterns of tooth wear reflect dietary and cultural differences with more rapid anterior tooth wear in the coastal dwelling Kaurna hunter-gatherers than in the Narrinyeri fishermen. The tooth wear data also confirm Murphy’s (1959) model of adaptation to loss of interalveolar hei ht b compensatory maxillary and mandibu ar a veolar bone changes. Mur hy’s model has been extended by the ad I fition of a more extensive series of craniofacial measurements, which suggest that this compensation is least effective in very muscular individuals with rapid posterior tooth wear (Narrinyeri males) and in relatively retrognathic individuals with rapid anterior tooth wear (Kaurna females). The complexities of the masticatory system are most evident in the relationships between both the patterns of tooth wear and craniofacial morphology and the morphology and pathology of the temporomandibular joints. The determinants of joint morphology are not well described, and although the studies described here (Richards, 1987) provide evidence of associations between aspects ofjoint morphology and both tooth wear and facial form, a comprehensive model of the determinants of joint morphology has not emerged. The factors that determine the nature and extent of joint remodelling are also poorly
R
Y P
described. Both the articular eminence and mandibular condyle show a e-related changes, with eminence heig t being smaller in older individuals, supporting the general conclusions reached by Seward (1976), and the frequency of condyle remodelling increasing with age. In addition, condyle remodelling was more commonly seen in individuals with relatively rapid anterior tooth wear, supporting the obvious conclusion that functional differences should be associated with differences in the pattern of joint remodelling. Many questions about the determinants of joint morphology are as yet unanswered, however. A clearer idea of the factors involved in the development of pathological joint changes in these groups has emerged from this series of studies (Richards and Brown, 1981b; Richards, 1988).Not only are the changes clearly age-dependent, but they are seen much more frequently in the groups showing the least effective mechanisms for compensating for rapid tooth wear (Narrinyeri males and Kaurna females) and in groups showing very rapid posterior tooth wear (Narrinyeri males and females). In addition, individuals with certain facial types (small ramus dimensions and either large facial profile angles and small occlusal plane angles or large occlusal plane angles and small facial profile angles) were very likely to be affected, indicating that both dental and facial factors were associated with the development of degenerative lesions of the temporomandibular joints. Despite the significant findings in this series of studies, investigations of this type are not without very important limitations. The nature of the available material means that most of the information was obtained from correlation analyses of cross-sectional data. This not only means that age-dependent variables must be interpreted carefully because of the possibility of sampling differences between the age groups, but also largely excludes the possibility of establishing cause-effect relationships between variables. For example, the observed correlation between articular eminence slope and the orientation of the occlusal surface of the ipsilateral third molars is a very important factor in the development of the helicoidal plane and is arguably an important factor in protecting the joint against excessive loading. Based on available information, however, the observed association provides no information about whether established joint
a
384
L.C. RICHARDS
morphology and the resultant pattern of mandibular movement is determining the direction of tooth wear or whether the joint is adapting to the pattern of movement determined by the teeth. The complex, multivariate nature of the questions addressed can also complicate both the design of studies such as this and interpretation of the results. The problems of missing data in studies of skeletal material and the combination of metric and nonmetric variables limit the usefulness of powerful multivariate statistical methods (Kowalski, 1972). Moreover, the very large sample sizes that would probably be required to demonstrate the significance of various, less common facial forms in the development of pathological joint lesions are either not available, or the necessary data collection would be prohibitively time consuming. Despite the difficulties in interpreting some of the information, these studies have rovided valuable support for some previous Rypotheses, the cast doubt on some other proposals, and t ey provided a rich source of promising new ideas for future investigation.
i
ACKNOWLEDGMENTS
This work was supported in part by the National Health and Medical Research Council of Australia and The University of Adelaide. The advice and assistance of Professor Tasman Brown, Dr. Grant Townsend, Professor Stephen Molnar, Mrs. Sandra Pinkerton, Mrs. Shirley Hastings, Dr. Diana Fabijan, Dr. Helen Bondarenko, Miss Fiona Rowett, Mrs. Wendy Schwerdt, and the Board and staff of the South Australian Museum are gratefully acknowledged. LITERATURE CITED Angel J L (1941) Factors in temporomandibular joint form. Am. J. Anat. 83:223-246. Barrett MJ, Brown T, and Macdonald MR (1963) Dental observations of Australian Aborigines: a roentgenographic study of prognathism. Aust. Dent. J. 8:418427. Begg PR (1954) Stone age man's dentition. Am. J . Orthod. 40:298-312. Behrand GD (1977) Quantitative evaluation of dental attrition (Abstract).Am. J. Phys. Anthropol. 47:117. Campbell TD (1925) Dentition and palate of the Australian Aboriginal. Adelaide: Sheridan Foundation. Cleland J B (1966)The ecology of the Aboriginal in south and central Australia. In BC Cotton (ed): Aboriginal Man in South and Central Australia. Adelaide: Government Printer, pp. 111-158. Duckworth WLH (1904) Morphology and anthropology. Cambridge: Cambridge University Press.
Giles E and Elliot 0 (1963) Sex determination by discriminant function analysis of crania. Am. J. Phys. Anthrop. 21:53-68. Hanau RL (1926) Articulation defined, analyzed and formulated. J. Am. Dent. Assoc. 13:1694-1709. Hinton RJ (1981) Changes in articular eminence morphology with dental function. Am. J . Phys. Anthropol. 54:439-455. Kowalsi CJ (1972)Acommentaryon the use ofmultivariate statistical methods in anthropological research. Am. J. Phys. Anthropol. 36:119-132. Koyoumdjisky E (1956) The correlation of the inclined planes of the articular surface of the glenoid fossa with the cuspal and palatal slopes of the teeth. J. Dent. Res. 35:890-901. Moffett BC (1974) The temporomandibular joint. In JJ Sharry (ed): Complete Denture Prosthodontics (3rd edition). New York: McGraw-Hill, pp. 56-104. Molnar S (1972) Tooth wear and culture-a survey of tooth functions among prehistoric populations. Curr. Anthropol. 13:511-526. Mongini F (1975) Dental abrasion as a factor in remodelling of the mandibular condyle. Acta Anat. 82: 292-300. Murphy TR (1959) Compensatory mechanisms in face height adjustment to functional tooth attrition. Am. J. Phys. Anthropol. 17:312-323. Porowski L and Bruska M (1978)Morphology of mandibular head of skulls from Uganda, Australia and Milicz. Folia Morphol. 37: 407-4 14. Richards LC (1983) Adaptation in the Masticatory System. Descriptive and Correlative Studies of a Precontemporary Population. Ph.D. thesis. The University of Adelaide. Richards LC (1984) Principal axis analysis of dental attrition data from two Australian Aboriginal populations. Am. J. Phys. Anthropol. 65:5-13. Richards LC (1985) Dental attrition and craniofacial morphology in two Australian Aboriginal populations. J . Dent. Res. 64:1311-1315. Richards LC (1987) Temporomandibular joint morphology in two Australian Aboriginal populations. J. Dent. Res. 66:1602-1 607. Richards LC (1988) Degenerative changes in the temporomandibular joint in two Australian Aboriginal populations. J . Dent. Res. 67:1529-1533. Richards LC and Brown T (1981a) Dental attrition and a e relationships in Australian Aborignals. Archaeol. ys. Anthropol. Oceania 16:94-98. Richards LC and Brown T (1981b) Dental attrition and degenerative arthritis of the temporomandibular joint. J . Oral Rehab. 8:293-307. Richards LC and Brown T (1986) Development of the helicoidal plane. Hum. Evol. 1:385-398. Scott EC (1979)Principal axis analysis of attrition data. Am. J . Phys. Anthropol. 51:203-212. Seward FS (1976)Tooth attrition and the temporomandibular joint. Angle Orthod. 46t162-170. Taplin GT (1874) The Narrinyeri, an account of the tribes of South Australian Aborigines inhabiting the country around the lakes Alexandrina, Albert and Coorong, and the lower part ofthe Murray River: Their manners and customs. Adelaide: Sawyer. Tindale NB (1974) Aboriginal tribes of Australia. Canberra: Australian National University Press. Townsend GC and Brown T (1979) Tooth size and characteristics ofAustralian Aborigines. Occ. Papers Hum. Biol. 1:17-38.
PI
